Manufacture of alumina hydrate



lM9y'14, 1935. A FLEISCHER 2,000,939

MANUFACTURE VVOF ALUMINA HYDRATE Filed July '7, 1933 2 Sheets-Sheet l .4N/fallar! 345/6 ALI/ff wrox/pf /Ef gra/ventola May14,1935. A. FLEISCHER f 2,000,939

MANUFACTURE OF ALUMINA HYDRATE Filed July 7, 1935 2 sheets-sheet 2 gmc/nto@ Patented May 174, 1935 poratonvof'Delaware v Y Application July 7, 1933," serial- No. 679,309 1 3 Claims. 101.2341435 Y MyV invention relates Vto the manufacture of `alumina hydrate and has vfor its object to provide an eiiici'ent process for manufacturing` alumina'hydrate from an insoluble basic alum as j a starting material.

alkali metal constituentof the alum.

It is known that a basic alum canjbe treated with ammonium' hydroxide with the result of a* reaction between the sulphur trioxide component of thebasic aluminumv sulphatev constituent of the basic alum and the formation of alumina hydrate and a solution of the ammonium sulphate formed by the union of the ammonia with the sulphur trioxide and in the case Where the basic alum isa potash or sodium alum't'nefsolution -will alsofcontain potassium or sodium sulphate 4but 'while this reaction is, as I have said, av known reaction, it has not, so far'as I ani-aware, been developed into a practical manufacturing process owing, mainly, that in carrying'out the" reaction with an 'excess of ammonia, no economical and technically feasible' provision was made to prevent losses of ammonia' in the furtherv treatment' of the reaction mixture Vand my invention consists, generally speaking, in the fo1` lowing` progressive steps: Y

First-I thoroughly mix the basic alum, which should be in a state of fine division, with a'solution of ammonia (ammonium hydroxide) containing ammonia in excess of `that equivalent to e 'the sulphur trioxide with which it is to reactto an amount of approximately 18% for solutions uplto cencentrations of 12% ammonia, by weight. The solution during this reaction should be maintained at temperaturesabove C. andprefer Eably approximately 1l0C. andthe reaction ywill be completed in approximately'onel hour and, under the 'conditions specified, substantially all of the basic-alum will be converted into insoluble alumina hydrate and a,` solution of sulphates vtwhich in the case that the basic alumvisan amimoniufn alum will consistentirelyv of ammonium sulphate andiin cases where the basic alum is an alkali metal 'alum theresultant solution.- will containtheV Vsulphates of ammonia and of'th The second stepof my process consists in boil'- ingV oir from theA solution obtained by the -above describedltreatment all'the ammonia still present as suchin the solutionby reason-ofthe exces'sof ammonia in the ammonium hydroxideYK usedvv for the treatment of the valum andthe recovery of thisammonia:y Where the temperature of fthe solution has been-raised?` to a V'point of approxi-l mately 1109"C., the heatofthe solutionitselflwill v'volatilizeand driveoii'fall -thisfex'cess ammonia. 1

Yity of autoclaves and by aprocedure in which rthe' If fa' lowertemperature'has been maintained durL "ingfthe reaction', itl may "be necessary to heatthe solutionand/or toapplya slightvacuum. j

Y The third step of o my'y process'cbnsists fin sep' arating the` insoluble 'alumina' hydratev frojm ithe' sulphate solution which may be accomplished' in any convenient" wayv but,".pref'erably, Iiirstr subject fthe` products of 'the reaction, that' is; the" alumina lhydrate and sulphate V47solution orf solutionsyjto a "thickening `treatment'j which "may 1 be" effected in any well-known form", of thickenerfr Aand their *treatY fthe" thickened.L vproductj of :this 1 treatment 1 to filtration in o order to L,eilec'zt QaIiferr'" tirei separation of the alumina hydrate'y fronthe l sulphate solution or solutions. The sulphate"so-Lf.,A lutions 1lrfWIfl fromjthe thickenerandlter "will:

ordinarily be treated forthe recovery therefrom of the sulphates.

Whileimy'invention may beV practiced l-bycl'iai ing the'A basicY alum" and previously'formedfainf moniurn hydroxide into theautoclaye andbylreyl .y covering-the, ammonia gas driven QE 'from thefref action; mixture in anabsorption tower, it ispreff'v erably-practiced in a` 'plant comprising apluralfff autoclaves are i charged with an aqueous'suspen# sionj of abasicalum towhichannnonia; gasis ir-AA troduced` to; yform' with "the Water. ammonium hyk droxide 1. and; by a further? procedureT in 'which af ter vthe completion of thereaction in 'theiaut cla'veftheammonia" gas driven off from thelauto-,ff

clave delivered directly kto,` ya. second'Aautoclavel Y charged Vwith ran aqueous'suspension'oi basic aluniA and' to whichjaiter the:r absorption iny the"'wa,ter" of the ammonia 'gas drivenofifrom' the iirst auto'f bringjthefprgduced ammonium hydroxide to the: propersength'for thecompletin-oi the reac" tion inthe second" autoclave k:from whiych;` again, the uncombine'dammonia-,gas is"d rivenoff andff re-"absorbedin another charged autoclave. 'I'hei advantages ofmy'prefere'd irletlidhf pfcti as ameans for:heating the `aqueous suspension-"oilV hydroxidecompont of'the A'autoclave' charge.: My=inventionwillj'be'perhejps better {inder'sto as "'desbribdflin# connection iwith'r/ the diagram:

35 g clave; additional f ammonia :Y gas is 'supplied toV 'f .5 an autoclave is directly charged with finely divided basic alum and previously formed ammonium hydroxide and in which the excess ammonia content in the charge of the autoclave, after the completion of the reactionis recovered as ammonium hydroxide in an absorption tower, while Figure 2 I have illustrated a plant adapted for the practice of my process in the preferential wayin which the autoclaves forming part of the system are charged initially with an aqueous suspension of the basic alum tolwhich ammonia gas is supplied to form ammonium hydroxide in the autoclaves, from which autoclaves, kafter thel rej action is complete, the excess ammonia gas is diven off and conveyed directly to an autoclave I freshly charged with an aqueous suspension of the basic alum to initiate in said second autoclave the formation of an ammonium hydroxide solution which is brought to proper strength by the admission to the autoclave of ammonia gas from an independent source of supply, and showing a combination lay-out of apparatus for the practice cf the process. VIn Figure l of the drawings, A indicates an autoclave. The autoclave should be formed of or lined with a corrosion resisting 'material, such as lead, and, as shown, is provided with a steam jacket as A1 and with a stirring apparatus indicated at B. I have indicated the top of the autoclave as of contracted diameter and rprovided with baffles indicated at C, to

trap any mist of solution escaping from the autoclave with the ammonia gas. lAt A2 I have indicated a man-hole through which, as indicated,

basicalum and ammonium hydroxide can be` 40 introducedV into the autoclave from reservoirs ,indicating a valve in said conduit) leading from `the bottom of the autoclave to a thickener indicated at Lhaving a launder at its top, indicated at I1, and'provided with rakes at its bottom, as indicated at J. From the bottom ofthe thickener, a conduitK leads to a filter, indicated at v`L,-which, as conveniently indicated and as preferably used, isa vacuum filter but which, of course, can be of any type. Conduits M and M1 lead fromv the launder and from the filter and X connect with a reservoir for the sulphate solution or vsolutions indicated at N. VThe aluminahydrate is, of course, withdrawn from the filter, as indicated. I have indicated at O a conduit leading from the absorption tower G to the reservoirE,indicat 30 iing that the ammoniumhydroxiderecoveredistobe used in connection with fresh ammonium hydroxidek for the treatment of further bodies of basicV alum.

In operation, the autoclave A is charged with a `A basic alum in a state of vfine division, preferably as a moist iilter cake and with a solution of ammonia (ammonium hydroxide) which solution should contain ammonia in excess of that which is theoretically equivalent to the sulphur Ytrioxide -`component of the aluminum sulphate constituent of the basic alum. The excess of ammonia can Y be varied considerably but, for goodpractical working conditions with solutions of ammonium hydroxide Vup to 12% ammoniaV concentration, I

prefer` to useabout- 18% over that theoretically required. A practical charge for the autoclave are the proportions of lbs. of a wet filter cake of basic ammonium alum, preferably manufactured in a continuous autoclave supplied with steam as a heating medium, and containing 33.3 lbs. of alumina, 34.8 lbs. of sulfur trioxide combined with the alumina, 14.3 lbs. of ammonium sulfateand 30 lbs. uncombined moisture, and 178 lbs. of ammonium hydroxide, containing 9.8% ammonia by weight, which allowing for the moisture content of the cake forms an 8% ammonia solution.

At concentrations higher than 12% of ammonia, the excess of ammonium hydroxide will be controlled by two factors, both of which influence therate and extent of the reaction, and which are, first the swelling of the alumina hydrate and secondly, the solubility of the sulfates formed in the reaction.

The alumina hydrate obtained from this reaction contains, after filtration and removal of the suliatesolution, free moisture to the extent of to 200% of its dry weight, depending on the basic alum, the ammonia concentration, and

the reaction temperature. Above 12% ammonia concentration and with 13% excess ammonia, the amount of water in the ammoniumhydroxide becomes insufficient to satisfy the degree of swelling of the alumina hydrate or to dissolve the sulfates formed in the reaction, causing the reaction mixture to assume a pasty form which is dimcult to agitate and stir, and in whichV thek reaction fails to go to completion.

With concentrated aqua ammonia, density of 0.90, it is necessary to use from 250% to 300% excess of ammonia.

vAfter the introduction of the alum and ammonium hydroxide, the autoclaveshould be closed and the mixture Vkept in agitation by the stirring apparatus B and maintained at a proper reactive temperature which should not ube less than 60 C. and which, preferably, should be approximately 110 C. because at this temperature all of the ammonia remaining in solution after the reaction is completewill be practically drivenoif from the autoclave when the conduit F is opened, as by the valve 'L to permit the ammonia to pass into the absorption tower G from which, as indicated, the solution of ammonia recovered may be conveniently passed to the reservoir E. After the ammonia has been eliminated from the solution in the autoclave the conduit I-I is opened as by means of the valve h and the contents of theautoclave passed to the thickener I, from which the greater part of the solution separated from the alumina hydrate passes through the launder I and pipe M to the reservoir N. The thickened mixture of the alumina hydrate and sulphate solution is then passed through conduit K to the filter L, where the remaining sulphate solution is separatedy from the alumina hydrate and passed, as indicated, to the reservoir N,

' while the alumina hydrateis drawn from the filter as indicated and is a finished article of manufacture. v

Referring now to Figure 2, those portions of the diagrammatically illustrated plant which are identical with those indicated in Fig. 1, are 'indicated by the same reference letters except that the second autoclave illustrated in Fig. 2, has been designated, for convenience, by the reference character a. In this plant the storage tankv for ammonium hydroxide, shown at E in Fig. 1,1 is notpresent nor is the absorption tower indicated in Fig. 1 at G. Thenew elements of the plant hydroxide solution is altopochemical reaction,V i.k e., a reaction occurring between a solid and ya consist in a storage tank for anhydrous am-VV monia, indicated at R, and a manifold indicated at P. This manifold is connected with the tank R by a pipe S, provided with a valve s and is connected with the tops of each of the autoclaves by means of pipes F1, provided with valves indicated at f1 and the manifold is also connected with the lower portion of each autoclave by pipes indicated at Q, provided With valves q. I have also indicated at T a receptacle for water, communicating conduits Tl leading to the autoclaves A and a and to any other autoclaves which may be included in the plant.

My preferential method for Which the plantV indicated in Fig. 2 is especially designed, involves the preliminary charging of the autoclaves with finely divided basic alum and Water and the basic alum being held in suspension in the water by agitation, I feed into the lower part ofthe autoclaves ammonia gas derived primarily from the storage receptacle R. and delivered through the pipe S, the manifold P andpipes Q, as, for example, When a plurality of autoclaves arepused,

the ammonia for the autoclave A is supplied inA this Way and, when the reaction is complete in the autoclave A, the ammonia driven oi from the autoclave is, by openingthe valve f1, delivered l through the pipe F to the'fmanifold P and through the manifold P and the pipe Q, the valve q of lwhich is open,V delivered into the aqueous suspension content in the autoclave a in which it is, of course, absorbed into the Water. When the tank A is exhausted of its ammonia, the valve f1 is closed and the valve s in pipe S opened so that ammonia is delivered directly from the tank A R through-the manifold and through the pipe Q into the autoclave a so as to raise the strength' of Ythe solution of ammonia to the desired point, after which the valves s and qare closed and the reaction permitted to continue in the autoclaveV a to completion. While this reaction is going on in autoclave a, autoclave A has been discharged and re-charged With an aqueous suspension of basic alum and, when the reaction is complete in autoclave a, valves are manipulated as described so that the ammonia driven off from the autoclave a. is first admitted to the autoclave A and then additional ammonia delivered through the manifold to the autoclave A. In all other respects, the operation of the plant indicated in Figure 2, is the same` as that indicated in Figure 1.

It is to be noted that the reaction between the reagent Yin solution. `At no stage of the reaction is any alumina dissolved in the reagent solution.

'Ihe easy filtering quality of the produced alumina hydrate is determined entirely bythe crystalline state of vthe finely divided insoluble basic,

alum starting material. The actual reaction is thus readily-listin guished from the reaction of ammoniawith Water soluble amphoteric metal salts where' it is necessary .to control the excess and concentration of the ammonia and the hydrogen ionconcentration of the solution. In this case a gelatinous precipitate is obtained. While this :form` may be readily filtered and handled on the lablui oratory scale required in analytical determinations, such a precipitate is handled on a commercial scale only at great cost, far in excess of an allowable gure'for the cost'of producing alumina hydrate on a commercial scale with a-viewto Vthe manufacture of a pure tion.

Having now described my invention, fwhatfI claim as new and desire to secure by LettersVv Patent, is:

ore for electrolytic reduc- 7 1. The method of producing alumina hydrate which consists in treating in a closed container a suspension of nelydivided basic alum in ammonium hydroxide containingrammoniain excess cf the amount equivalent. to the sulphur trioxide.

component combined with alumina in basic alum at temperatures above 60 C. to effect the decomposition of the basic alum with formation of vinsoluble alumina hydrate and a solution of `ammonium sulphate and alkali metal sulphate if a1- kali metal sulphates exist in the basic alum and of ammonia in solution, then driving oil? from said solution the uncombined ammonia held in solu tion therein and recovering said ammonia by condensation and absorption and finally separating the alumina hydrate from the ammonia free sulphate solution.

2. The method of claim l in which the reactive ammonium hydroxide solution is formed in the presence of an aqueous suspension of basic alum by introducingammonia gas to said aqueous suspension. l

3. 'memethodpf claim 1,111 which the uncombined ammonia held in solution after the reaction is completed is recovered by condensation and absorptionin a further` second body of aqueous suspension of basic alum.

' ARTHUR yFLEISCHER. 

